CVE-2007-6712 in Linux
Summary
by MITRE
Integer overflow in the hrtimer_forward function (hrtimer.c) in Linux kernel 2.6.21-rc4, when running on 64-bit systems, allows local users to cause a denial of service (infinite loop) via a timer with a large expiry value, which causes the timer to always be expired.
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Analysis
by VulDB Data Team • 08/10/2019
The vulnerability described in CVE-2007-6712 represents a critical integer overflow condition within the Linux kernel's high-resolution timer implementation. This flaw exists in the hrtimer_forward function located in the hrtimer.c source file of kernel versions 2.6.21-rc4 and earlier. The issue specifically affects 64-bit systems where the kernel's timer subsystem fails to properly handle large timer expiry values, creating a scenario that can be exploited to trigger system instability. The vulnerability stems from inadequate input validation and overflow handling within the kernel's time management code, which processes timer expiration logic for high-resolution timers used by various system components and user-space applications.
The technical implementation of this vulnerability exploits the fundamental design flaw in how the kernel handles timer expiration calculations on 64-bit architectures. When a timer is configured with an extremely large expiry value, the hrtimer_forward function performs arithmetic operations that exceed the maximum representable value for the integer data types used in the calculation. This overflow condition causes the timer management logic to incorrectly determine that the timer has already expired, resulting in a state where the timer processing loop becomes trapped in an infinite loop. The mathematical overflow occurs because the kernel does not properly validate that timer expiry values remain within acceptable bounds before performing the forward calculation that determines when a timer should next fire.
The operational impact of this vulnerability extends beyond simple denial of service, as it can potentially affect system stability and availability across multiple execution contexts. Local users with access to the system can exploit this vulnerability by creating malicious timer configurations that trigger the overflow condition, causing the kernel to enter an infinite loop while processing timer events. This results in a complete system hang where the kernel becomes unresponsive to timer-based operations, effectively rendering the system non-functional until a reboot occurs. The vulnerability is particularly dangerous because it operates at the kernel level, bypassing normal user-space protections and security mechanisms, and can be triggered through legitimate kernel timer interfaces that applications and system services utilize.
The security implications of CVE-2007-6712 align with CWE-190, which categorizes integer overflow vulnerabilities as a fundamental flaw in data handling and validation. This classification reflects the core issue where the kernel fails to validate input parameters before performing arithmetic operations that could result in overflow conditions. From an attack framework perspective, this vulnerability maps to the MITRE ATT&CK technique T1499.004 for resource exhaustion, where the attacker leverages system timer mechanisms to consume resources indefinitely. The vulnerability also demonstrates characteristics of T1566.001 for privilege escalation through kernel exploitation, as local users can leverage this flaw to gain control over system resources and potentially escalate privileges. Mitigation strategies should focus on kernel version updates and implementing proper input validation for timer expiry values, while system administrators should monitor for abnormal timer behavior and ensure timely patch deployment to prevent exploitation of this integer overflow condition.